Yeah you are fine to overclock. You could probably start at 4.3Ghz @1.3 volts. Sandybridge was well known for being able to handle quite a good voltage.
You will want to download a temp monitoring program like hwinfomonitor and a stress testing program, like real bench.
This is so you can overclock then stress test the system while watching temps. I wouldn't push the temp past 75C without doing a bit more research.